commit 0b9c27041e918cb4369f7a4fd1e3d217a438aef1
Author: John Lindgren <john@jlindgren.net>
Date:   Fri Oct 26 20:45:05 2018 -0400

    gl-spectrum: We don't need a visual with an alpha channel.
    
    This change was suggested by email without much extra info,
    but apparently fixes a BadMatch error for someone.
    
    If this causes trouble, don't hesitate to revert.

diff --git a/src/glspectrum/gl-spectrum.cc b/src/glspectrum/gl-spectrum.cc
index a91f241e1..7fd1f51fd 100644
--- a/src/glspectrum/gl-spectrum.cc
+++ b/src/glspectrum/gl-spectrum.cc
@@ -300,7 +300,7 @@ static void widget_realized ()
      GLX_RED_SIZE, 1,
      GLX_GREEN_SIZE, 1,
      GLX_BLUE_SIZE, 1,
-     GLX_ALPHA_SIZE, 1,
+     GLX_ALPHA_SIZE, 0,
      GLX_DOUBLEBUFFER,
      GLX_DEPTH_SIZE, 1,
      None